Migrant Hawkers emerging

At Ditchford, on a hot but windy afternoon my son located our first Migrant Hawker exuviae along with several Emperors. Flying were a few Emperors, Brown Hawkers with many females oviposting in the muddy banks, and the usual Damselflies including an Emerald, the first sighting here in over 7 years. I have always wondered why I have never seen Emeralds here.